Resistance to known antimalarial therapies is becoming an increasing problem and new therapies are therefore desperately needed. Upon infecting a host, the malaria parasite avidly consumes the host hemoglobin as its source of nutrients. Plasmepsin I and II are proteases from Plasmodium falciparum that are necessary during the initial stages of hemoglobin hydrolysis and digestion, which occurs in the .alpha.-chain, between Phe 33 and Leu 34, then other sites serve as substrates for hydrolysis as well. In culture, inhibition of plasmepsin by a peptidomimetic inhibitor is demonstrated as effective in preventing malarial hemoglobin degradation and in killing the parasite (Francis, S. E., Gluzman, I. Y., Oksman, A., Knickerbocker, A., Mueller, R., Bryant, M. L., Sherman, D. R., Russell, D. G., and Goldberg, D. E. (1994) EMBO J, 13, 306-317). Thus, persons of skill in the art expect that plasmepsin inhibitors will provide effective antimalarial therapy in humans.
Cathepsin D is a human protease in the endosomal-lysosomal pathway, involved in lysosomal biogenesis and protein targeting, and may also be involved in antigen processing and presentation of peptide fragments. The protease therefore displays broad substrate specificity, but prefers hydrophobic residues on either side of the scissile bond.
Cathepsin D has been implicated in a variety of diseases, including connective tissue disease, muscular dystrophy, and breast cancer. Cathepsin D is also believed to be the protease which processes the .beta.-amyloid precursor protein (Dreyer, R. N., Bausch, K. M., Fracasso, P., Hammond, L. J., Wunderlich, D., Wirak, D. O., Davis, G., Brini, C. M., Bucholz, T. M., Konig, G., Kamarck, M. E., and Tamburini; P. P. (1994) Eur. J. Biochem., 224, 265-271 and Ladror, U. S., Synder, S. W., Wang, G. T., Holzman, T. F., and Krafft, G. A. (1994) J. Biol. Chem., 269, 18422-18428), generating the major component of plaques in the brains of Alzheimer's patients. Consequently, persons of skill in the art expect that inhibitors of cathepsin D will be useful in treating Alzheimer's disease.
The present invention relates to peptidomimetic (hydroxystatine amides and hydroxyphosphonates) analogs and their inhibitory action against aspartyl proteases. More particularly, the invention relates to the identification of such compounds that display selective inhibitory activity against plasmepsin and cathepsin D. Although statine-containing peptides are known which inhibit aspartyl proteases (Shewale, J. G.; Takahashi, R.; Tang, J., Aspartic Proteinases and Their Inhibitors, Kostka, V., Ed. Walter de Gruyter: Berlin (1986) pp. 101-116; U.S. Ser. No. 08/743,944, filed Nov. 5, 1996, which is hereby incorporated by reference in its entirety), there are only a few selective inhibitors for cathepsin D (Lin, T.-Y.; Williams, H. R., Inhibition of Cathepsin D by Synthetic Oligopeptides, J. Biol. Chem. (1979), 254, 11875-11883; Rich, D. H.; Agarwal, N. S., Inhibition of Cathepsin D by Substrate Analogues Containing Statine and by Analogues of Pepstatin, J. Med. Chem. (1986) 29 (2519-2524)), and for plasmepsin (Silva, A. M. et al., Structure and Inhibition of Plasmepsin II, A Hemoglobin-Degrading Enzyme From Plasmodium falciparum, Proceed Natl Acad Sci, 1996, 93, 10034-10039).
The present invention also relates to the solid phase synthesis of such peptidomimetic analogs.